Besides parameters resolution and shitty envelopes, there's 2 main things that make a stock prophet 600 sound different than a prophet 5 I think:- You can't mix the 2 oscs at full volume, because of the single pot mixer. That means you can't really overdrive the filter like you can on a P5.- You can't fully open the filter without adding envelope, modulation or keyboard tracking, that's why the P600 is known to have a kinda 'dark' sound I think.

Those 2 are software limitations, and sometimes I wonder if they weren't added on purpose, so that the P5 would still have an edge on raw tone!

By the way the P600 DAC is wired as 14bit (from a 16bit capable chip), that's pretty good for a synth from 1983. The only problem is the CPU was so slow, they chose to only use the top 6bit for most parameters! A software limitation again...

I love my 600 but I'd love it even more with improvements. Not sure of the scope of that project but ideally a noise source would be added. I'd be happy with a digital one...

One thing that's added quite a lot of spice to my prophet 600 is adding an external (i.e., much faster) LFO source. I use the LFO out on my MF Ring Mod, but there are any number of ways to skin that cat. You can hear the results in a number of the sounds on this demo:

I think it's been covered in another thread, but since the topic of a firmware upgrade for the Prophet 600 has come up, let me point you to this thread over an Anafrog (in french, but Google translate does a half decent job): http://forum.anafrog.com/phpBB/viewtopi ... 0a3129efd8

This project is distinct from what I was working on, but basically supersedes my project. The last couple posts on my blog cover some of the functional details. No MIDI or sequencer/arp functions yet, but all the basic synth functions are implemented. Probably the coolest upgrades so far are different LFO shapes (random!) and mixing oscillator A and B so that the filter can be overdriven.

The author of the project has been quiet for the last couple of weeks, hopefully because he's busy finishing the firmware and about to release a beta!

It's a CPU (a $30 Teensy++ 2.0 board) and (open-source) firmware upgrade. I did the simple soldering mods to the board, loaded the firmware and installed it on my P600 a couple days ago. Some (but not all) of the improvements:

2) Faster envelopes (selectable among four choices). They still aren't lightning fast but they are better.

3) Better LFO (selectable among three modes: slow, medium, and fast).

4) More LFO modes, including S&H and noise.

5) The filter envelope control and Poly-Mod filter control are now capable of doing negative envelopes.

6) The oscillator blend control is now the level control for OSC A, with OSC B level controlled by Glide knob (arpeggiator Speed knob now controls glide amount, unless the arpeggiator is being used). The oscillators can now overdrive the filter if they are set above the midway point.

7) Selectable pitch wheel range (minor 3rd, 5th, octave).

8) Mod wheel (or is it pitch wheel?) can now control filter cutoff.

9) MIDI cc control of all parameters.

This is still in beta phase, but thanks to the hard work and generosity of GliGli, we Prophet 600 owners now have a new beast on our hands!